Control of electrical contacting elements



June 7 1949. M, KNAPP 2,472,709

comm, OF ELECTRICAL commcwme ELEMENTS Filed Feb. 6, 1947 2 Sheets-Sheet'1- By H. M. KNAPP A T TORNE Y June 7, 1949. H. M. KNAPP CONTROL OFELECTRICAL CONTACTING ELEMENTS 2 Sheets-sheaf 2 Filed Feb. 6. 19 4? STUDAND CONTACT WEAR INCHES INVENTOR H. M. KNAPP 696. M

ATTORNEY Patented June 7, 1949 CONTROL OF ELECTRICAL CONTACTING ELEMENTSHarry M. Knapp, Scotch Plains, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication February 6, 1947, Serial No. 726,839

9 Claims. 1

This invention relates to means for controlling electrical contactingelements and more particularly to improvements in and relating to meansfor controlling the movable contact springs of electromagnetic relays.

The present invention is based upon the new and simple concept ofproviding that in an electrical contacting device, such as the familiarelectromagnetic relay, all movable contacting elements, such as movablerelay contact springs, be tensioned to normally make contact with therelatively fixed elements with which said movable elements cooperate,that the force required for the said contact closure be derived solelyfrom the self-tension of the said movable elements and that thecontacting element actuating means be capable of selectively separatingnormally closed pairs of elements in either the operated or unoperatedcondition of the contacting device or in both conditions to therebyeffect the desired switching operations from the said plurality ofcooperating elements.

Previously, in relays having a plurality of movable and fixed contactsprings, mating springs have been employed in such combinations as normally open pairs, normally closed pairs, make before break combinations,break before make combinations and other transfer combinations andvarious arrangements of two or more of these combinations, the normalcondition referred to being the condition of said contact springs whenthe armature of the particular relay is unoperated. These variouscombinations, appearing iorinstance on one relay, have been actuated bymeans of an insulating member, such as a card or spring separator studassembly, both of which are well known and which have been adapted to bemoved by the armature of the relay to perform in turn the indicatedcombination spring operations. It has been the practice in some cases toprovide normally closed pairs where the movable or armature spring ofthe pair is tensioned to normally contact the fixed spring of the saidpair by reason solely of its own tension and the operating card, whenmoved by the armature, moves said movable spring away from the fixedspring to efiect the break of said pair. In the same or other relaysnormally open pairs have been provided where the movable spring of thepair is normally in the open condition such that the operating card is"required to overcome the natural self-tension of the movable springwhen deflected to effect the required closure of the pair. This occursin either normal or operated condition depending on the nature of thecombination desired for the operated condition. Likewise it has been thepractice to provide all normally open contacts free of external forcesin the open position and to provide normally closed contacts where themovable spring is tensioned to either open or closed position when underno external forces.

It has been known previously that a movable spring which normally byreason of its own tension is open and is moved against its ownresilience is required to be moved or urged beyond closure in order toefifect a satisfactory contact pressure. It has been known that the rateof loss of this contact pressure with contact wear and wear of the cardor separator stud is objection ably rapid. This condition hasnecessitated one or more of at least three general types of correc-.tive measures; namely, starting with large initial contact pressure topermit appreciable wear before the contact pressure has decreased to theminimum allowable, or constant readjustment of the relative openseparation of mating contacts to permit closure earlier in the armaturestroke with attendant increase in contact follow effective to overcomethe lost pressure due to wear, or increasing the armature travel tocompensate for the Wear, or various combinations of these measures.

It is the primary object of this invention to eliminate substantiallythe necessity for the above corrective measures. The present inventioncontemplates a simple means for eliminating the required initial highcontact pressure, eliminating necessity for constant or frequentreadjustment of contact springs and elimination of the requirement forincreased armature travel. It has been discovered that the rate of lossof contact pressure with wear of contacts or contact spring actuatingmeans for normally closed contacts, where the closed condition is duesolely to the self-tension of the movable spring, is considerably lessthan the rate of loss with the'same sources of wear for normally opencontacts, where closure is the result of force applied externally of themovable spring. The present invention provides that not some, nor most,but all movable contact springs be tensioned normally to make closurewith the required contact pressure. and that the normally open, normallyclosed, etc; combinations previously mentioned are to be effected bymeans of a card for selectively separating the normally closed contactsprings either in the unoperated or operated positions of the armatureactuated card. This simple arrangement enables from a more practicalstandpoint the assembly oi springs which are preset for the requiredcontact pressure by being given a bend or deflection prior to assembly.By employing the above-mentioned type of spring actuation the rate ofstiffness build-up of the movable springs is low thus requiring asubstantial set or bend for a given contact force. Because of this largeset less accuracy is needed in an initial bend or deflection prior toassembly to insure the required tclerancy of contact pressures afterassembly. This difierence m enough to make more practical thepretensioning of springs prior to assembly whereas with previously usednormally open springs this practice was not advisable and consequentlythe tensionlng had to be done by adjustment alter assembly, except incases where the initial contact pressure tolerance was large enough topermit said tensioning prior to assembly. I

Relative to the previously outlined prior art regarding relay contactsprings, the said operating cards or separator stud assemblies usedtherewith generally have been positioned relative to the contact end ofsaid springs and the supportingends of said springs such that upon ac=tuation of these springs, by the said cards for instance, the movablesprings were bowed due to the contact follow necessary to insuresatisfactory contact pressure. This condition of bow= ing of the movablesprings created a relative slid ing of the mating contacts due to theconcave or arranging all closures of contacts to be made solely due toself-tension of the movable springs to position the contacting forcedirectly at the contact area. This prevents any undue bowing of eitherspring due to the movement of either spring after closure previouslyrequired to insure contact pressure and limits the possibility of bowingof contact springs on opening operations. It is apparent that if thesprings on contact have been freed of any excessive bending or bowingthere will be little tendency for mechanical oscillation upon initialcontact closure and thus a source of initial contact chatter will beeliminated.

Bifurcated springs are old in the art but one feature of such springswhich has been a constant source of requirement for improvement has beenI the high degree of relative mechanical dependconvex nature of the bowin the movable spring and produced potential mechanical oscillations inthe bowed spring which were materially re sponsible for initial contactchatter. It has been discovered that this sliding action is largelyresponsible for mechanical interlocking of pitted contacts, the pittingbeing caused, as is well known, by arcing at the said contacts onclosure and break effecting an exchange of contact material from onecontact to its mating contact depending on the polarity of the arcing orattendant current discharge. One of the pitted contacts generallyassumes a built-up conical configuration having jagged sides, the matingcontact generally assuming a configuration resembling a conicaldepression having Jagged sides. Any lateral or transverse or slidingmotion between these mating contacts in the closed position tends tointerlock the respective jagged edges and cause mechanical locking ofthe contacts. Several methods have been devised for limiting thebuildmentioned mechanical locking condition and thereby relieves thenecessity for using large restoring forces to overcome same. Theinvention also substantially eliminates storing up in the spring ofpotential mechanical oscillations to thereby effect substantialelimination of a large source of initial contact chatter. This meanscomprises simply arranging the contact spring actuating member, such asa card or separator, to exert its moving influence on the movablesprings as near the contact area as possible and ence of thebifurcations. The slots in these springs have been required to beshallow for separator stud operated springs because the stud generallyhas been positioned between the contacts of the springs and the springsupport thus mechanically limiting the depth of these slots. It isapparent that shallow slots permit the bifurcations to interactmechanically to a greater extent than for a deep slot and consequentlyprevious types of. bifurcated springs have not exhibited the bestdesirable degree of mechanical independence of the bifurcation. Forinstance, a small particle of dust or dirt under one bifurcation couldeasily effect non-closure of the other due to the close mechanicallinkage between same resulting from a shallow slot. This condition hasdemanded large contracting forces to overcome the latter tendency.

An incidental feature of the present invention is to create greatermechanical independence of the bifurcations of contact springs. Thepresent invention, by providing actuation of the springs at or near thecontact area, permits, as one example, the card or other operatingmember to be placed at the free ends of said'springs, which arrangementenables one to make the bifurcation slot as deep as desired thus adding,to an already improved situation, a substantial increase in theindependence of the bifurcations. It is apparent that large contactpressures formerly required to insure satisfactory contact may now bereduced since no longer is it necessary to overcome resistance toclosure movement represented by dirt or dust on the contact of onebifurcation.

The foregoing objects of the invention are further explained in thesubsequent description of an exemplary embodiment of the invention, thefollowing being general descriptions of the various figures of thedrawings which form a part of the said description:

Fig. 1 shows the armature'side of a, well-known type of relay embodyingthe present invention.

Fig. 2 is a side elevation of the relay shown in Fig. 1 and mayrepresent either side of said relay.

Fig. 3 is a view showing the contact spring pile-up side of the relay ofFig. 1.

Fig. 4 is a magnified view of the contact end of the relay of Fig. 2 andillustrates an unoperated condition of the armature of said relay.

Fig. 5 is similar to Fig. 4 except that it shows an operated conditionof the armature.

' Figs. 6 and '7 are views similar to Figs. 1 and 2, respectively, andshow a modified construction embodying the invention.

Fig. 8 is a set of curves illustrating an outstanding advantage inutilizing the invention.

These curves will be referred to later with suitable comment.

Figs. 1 through 5 show a familiar form of electromagnetic relaycomprising a core I, heel piece 2, armature 3 pin hinged at 4 to hingebracket 5 clamped to heel piece 2 and held to the extension 5 by meansof leaf springs 6, a spring pile-up assembly i'l comprising relativelyfixed spoolhead springs I, 8 and 9 having lugs l which engagespoolheadII on one end of coil l2 and relatively movable or armature springs l3,l4, l and 16 held together by means of screws I8 and operating cards l9each fixed and guided by an outer balance spring 20, inner balancespring 2| and a buffer spring 22 welded or otherwise fixed to thearmature 3 at area 23 and provided with an adjusting screw 24 carried bythe armature 3.

In Fig. 4 are shown the operating ends of the contact springs on oneside of the relay, the drawing being intended if desired, to representthe structure on the other side of said relay as well. Fig. 4 indicatesthe normal or unoperated condition of the relay, of card l9 and ofarmature contact springs l3, l4, l5 and Hi. In this relay all of thearmature springs are tensioned to make contact with their respectivemating spoolhead springs with satisfactory contact pressure when noexternal force acts on the movable springs. That is, if card 19 were notpresent armature spring l3 would contact spoolhead spring I, as shownsince this is a break pair, armature spring l4 would contact spoolheadspring 8, shown separated by intervention of the card [9 because this isa make pair, and armature springs and I6 would contact spoolhead spring9, armature spring l5 being shown in contact and armature spring 16being shown separated since this is a make and break combination.

The card I9 is positioned in outer balance spring by means of thereduced end 25 of card l9 entering a suitable rectangular hole in theend of outer balance spring 20 as shown more clearly in Fig. 3. The freeend of the inner balance spring 2i is shown most clearly in the part ofFig. 1 wherein parts of buffer spring 22 and armature 3 are broken away.A rectangular slot 26 in the end of inner balance spring 2| is adaptedto fit snugly under the'top shoulder of the card l9-as shown in Fig. 2.The buffer spring 22, attached to armature 3 along with its adjustingscrew 24, is provided with a depending end portion 21 which is adaptedto prevent the card i9 from slipping out of the slot 26 in the innerbalance spring 2|. These balance springs 20 and 2 i, as well as thebuffer spring 22, are of resilient character in order to hold the card[5 as shown and also to permit movement thereof by armature 3.

The outer balance spring 20 is tensioned to urge the card l9 upward tothe position shown in Fig. 4. The buffer spring 22 urges the card l9downward as viewed in Fig. 4. The inner balance spring 2 I urges the,card [9 upward as viewed in Fig. 4 an amount substantially equal tothat exerted by the outer balance spring 20. The relative forcesproduced on the card H! by the respective balance springs may be dividedbetween them in any proportion desired.

From the status of Fig. 4 to that of Fig. 5 it is seen that the card' 19has engaged the end of armature spring I3 and has pushed it away fromcontact with spoolhead spring 1, this movement being against the naturaltension in armature spring l3. On the other hand, card 19,

7 ing of the preceding pairs.

which previously held armature spring ll out of contact with spoolheadspring 8, has now moved so as to permit spring M to make contact withspring 8 under its own tension. The action of the make and breakcombination of springs l5, l6 and 9 is merely a combination of thefunction- Upon release of armature 3 the combined forces stored in thebalance springs 20 and 2|, the armature hinge spring 6, and the armaturesprings 13 and I5 will return the armature 3, card l9 and all springs totheir normal positions of Fig. 4.

The contact springs of the relay may be bifurcated for whatever lengthof spring is desirable since by the use of the invention the card [9 isshown as acting at or substantially at the contact area and does notinterfere with the cross section of these springs. As shown in the partof Fig. 3 wherein part of one of the outer balance springs is brokenaway, the armature spring l3 may be provided with a deep slot 28 whichwill permit the individual bifurcations 29 and 30 to be considerablymore independent of each other mechanically, and consequentlyelectrically as far as contact closure is concerned, than they would beif slot 28 were shallow as in previous types of similar constructionwhere the separator stud type of actuating member was placed between thecontact ends of these springs and the supporting pile-up assembly H. Aparticle of dust or dirt which might reside under bifurcation 29 wouldhave small tendency to interfere with or prevent bifurcation 30 makingadequate electrical contact with spoolhead spring 1. Consequently,

" less contact pressure is required with the proposed type of deepbifurcation than was required in the previous shallow type to insureelectrical contact.

As outlined previously, the rate of loss of contact pressure withcontact and card wear for springs which are normally tensioned toclosure by reason solely of self-tension of the movable spring isconsiderably less than of that for springs normally in the open positionwhen no external forces act thereon. In the former situation the loss incontact pressure is determined by the loss in tension in the armaturespring alone as wear occurs due to the fact that the spring approachesfurther to equilibrium and thus represents less potential contactingforce. In the other case the loss in contact pressure is due to the factthat the actual total movement of the spring by its actuating member isthe same but the effective contact follow is reduced by the amount ofwear.

The latter consideration as well as the previous discussion concerningthe prevention of mechanical interlock of contact, as well as theenabling of deep slotted bifurcations, all combine to materially reducethe contact pressure requirements for contact springs of such relays asare provided with the invention. The reduction is due to the use ofcontact springs which are all normally positioned to closure by reasonsolely of the selftension of the movable springs and which are actuatedby a card or separator stud or similar member acting substantially atthe contact area.

The simplicity of this invention in concept and in the manifestation ofthe parts and conditions necessary for its functioning make it readilyadapted to manufacture and assembly in or with standard relays andalleviates maintenance problems by eliminating mechanical interlock ofcontacts and necessity for frequent readjustment of springs tocompensate for contact and card or stud wear. The aforementioned smallloss of contact pressure with contact and card wearenables thepracticality of assembling pretensioned armature springs with anassurance that the specified tolerances for contact pressure are met.

A further advantage of arranging the card or stud to actuate the springssubstantially at the contact areas and arranging the springs to benormally tensioned to closure is that no excessive bending or bowing ordeforming o! the armature springsis necessary to insure contact pressureand even if a substantial amount is represented by the natural tensionof the armature springs the contacting force is still applied directlyat the contact area on closure. on break conditions the card or stud isarranged to apply its pushing force onthe armature springs at orsubstantially at the contact area. These provisions, as previouslymentioned, eliminate'the storing of potential mechanical oscillations inthe springs by not deforming them. Consequently no potential mechanicaloscillations can become dynamic to efiect contact chatter.

In Figs. 6 and 7 are shown two views of a relay similar to the onepreviously discussed. The relay of Figs. 6 and 7 embodies a modificationof the card and armature relationship whereby, instead of a bufferspring to position and actuate the card I9, the top shoulder of the cardi9 is provided with a recessed inner edge 38 which is adapted toaccommodate an upstanding tang it in the end of the inner balancespring. This positions the card 89 and also prevents it from slippingout of the spring assembly, it being noticed that the top end of thecard merely rests against the underface of armature 3. The armature 3comprises a broad end area 32 which may cover the entire width of therelay including the contact ends of all springs. The dotted portions ofFig. 6 indicate the general configuration of the undersurface ofarmature 3, numeral 33 designating recesses in the underface of armature3 which are provided to accommodate the armature ends of cards [9, asshown in Fig. 7. The other parts of the relay and their functions arethe same as for like parts previously discussed in connection with Figs.1 through 5. A hooklike end 35, as shown in Fig. 7, may be provided forthe card 19 to prevent the outer bufier spring from accidentally beingjarred from its retaining position on card l9.

Fig. 8, derived from test data, shows the rate of loss of contactpressure with card or stud and contact wear for relays having normallyopen contact springs and for those having normally closed contactsprings. Is is to be noted that curves A and B represent relays providedwith the invention whereas curve C represents relays according to priorart in that self-tensioned normally closed springs are not useduniversally. The curve C indicates that for previous types of normallyopen contacts the average contact pressure of say 25 grams is reducedrapidly to zero with contact and stud wear from zero up to say .013inch. Curve B indicates that an average contact pressure of about 23grams is substantially constant up to wear of about .013 inch, where itdrops abruptly to zero. If an average contact pressure of say 13 gramsis all that is required, curve A would suflice for the entire range ofwear of the old type of relay arrangement provided the invention isemployed. In addition it is apparent that the full depth of contactmaterial is used without requiring readjustment or replacement ofsprings because 8 the contact'pressure is substantially constant for say.013 inch which might very well be the depth of the contacts; whereas,according to curve C, the full depth of ".013 inch cannot be used sincethe minimum allowable contact pressure is exceeded making readjustmentor replacement of springs necessary before that amount of wear isreached. The minimum contact force, or pressure, is illustrated by curveD at about 10 grams. This curve D is an order of magnitude only andrepresents the neighborhood of the unsatisfactory operating zone. It isof course possible that this curve D can be at' any magnitude belowabout 20 grams and still indicate the point above mentioned. V

Having set forth the objects and purposes 0! the invention with adetailed description of how to apply same, I append claims which alonedefine the scope of the invention since many modifications,rearrangements, new aspects and other embodiments than the one disclosedherein by example will be suggested to those skilled in the art.

What is claimed is:

1. In an electrical contacting device, a plurality of relatively fixedcontacting elements, a plurality of relatively movable resilientcontacting elements cooperating therewith, all of the said movableelements being tensioned normally to make contact with respective fixedelements by reason solely of their own tension, actuating means, andmechanical means controlled by said actuating means'having shoulderedportions for selectively opposing the tension of said movable elementsto effect switching operations thereby.

2. In a relay, cooperating pairs of relatively fixed and relativelymovable resilient contact springs, each of said movable springs beingtensioned normally to make contact with the cooperating fixed spring ofthe pair by reason solely of its own resilient tension, an armature, andan operating member controlled by said armature having shoulderedportions for selectively opposing the tension of said movable springs toeflect switching operations thereby.

3. A relay having a plurality of relatively fixed contact springs havingcontacts thereon, a plurality of relatively movable resilient contactsprings having contacts thereon and adapted to make contact with thesaid fixed springs at respective contacts thereof, means for applyingthe contacting forces between respective contacts of said springs onlyat anddirectly at the contact area, the said means comprising tensioninginherent by reason solely oftheir own tension of all movable springsurging same to normal closure with said fixed springs, and additionalmeans provided with shouldered portions to selectively separate saidnormally closed pairs of springs.

4. A relay comprising an armature, relatively fixed contact springs,relatively movable resilient contact springs all tensioned normally byreason solely of their own tension to contact cooperating fixed springs,and a resiliently suspended member having shouldered portions actuatedby said armature and adapted, under the control of said armature and bysaid shouldered portions to selectively separate the said normallycontacting pairs of movable and fixed springs.

5. A relay comprising an armature, relatively fixed contact springs,relatively movable resilient contact springs all tensioned normally byreason solely of their own tension to contact cooperating fixed springs,and a resiliently suspended member actuated by said' armature, havingshouldered portions normally positioned to separate some contactingpairs of said movable and fixed springs and having other shoulderedportions effective when said member is actuated to separate othercontacting pairs of movable and.

fixed springs and to enable contact between springs of the pairspreviously separated by the said member when in its normal position.

6. A relay comprising an armature, a plurality of relatively fixedcontact springs having contacts, a plurality of relatively movableresilient contact springs having contacts, all of the movable springsbeing tensioned normally by reason solely of their own tension to makeclosure with the said fixed springs at respective contacts thereof, andmeans having shouldered portions controlled by the said armature,certain of its shouldered portions being disposed to separate at leastone of said closed pairs of springs when said armature is unoperated,the said means, when controlled by operation of said armature, beingeflective by said certain shouldered portions to release the separatedpair or pairs to permit same to make closure due to the inherent tensionof said movable springs and by others of its shouldered portions toseparate the remaining closed pairs of said plurality of cooperatingpairs of fixedand movable springs.

'7. In a card operated relay a relatively fixed contact spring havingcontacting areas, a relatively movable resilient contact spring having acontacting area and located on each side the said fixed spring, each ofthe said movable springs being tensioned normally by reason oi! its owntension to contact the said fixed spring at respective contacting areasthereof, a card having shouldered portions and an armature, the saidcard adapted, under the control of said armature, to selectively engageshouldered portions tl.-reof with the said movable springs substantiallyat the contacting areas thereof to selectively disconnect same from thesaid fixed spring. 7

8. In a card operated relay a plurality of relatively fixed contactsprings having contacting areas, a plurality of relatively movableresilient contact springs having contacting areas, each of said movablesprings being tensioned normally by reason solely of its own tension tocontact at least one'of said fixed springs at respective contactingareas thereof, a card having shouldered portions and an armature, thesaid card adapted, under the control of said armature, to selectivelyengage shouldered portions thereof with the said movable springssubstantially at their contacting areasto thereby selectively disconnectsame from said fixed springs.

9. In a card operated relay, a plurality of relatively fixed contactsprings having contacting areas on one of the ends of each, a pluralityof relatively movable resilient contact springs having contacting areason one of the ends of each, all of said springs being assembled in asuperimposed pile with all contacting areas at one end of said pile, anarmature and a card having shouldered portions actuated thereby, all oi.the said movable springs being tensioned normally by reason solely oftheir own tension to contact the said fixed springs at respectivecontacting areas, the said card adapted, under the control of saidarmature, to selectively disconnect contacting pairs of said springs byselectively engaging shouldered portions thereof with said movablesprings substantially at their contacting areas and selectivelydisconnecting same from the mating fixed springs.

' HARRY M. KNAPP.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 2,120,980Johnston June 21, 1938 2,178,656 Swenson Nov. '7, 1939 FOREIGN PATENTSNumber Country Date 511,092 Great Britain A118. 14, 1939

